Apparatus for reducing contamination of surgical site

ABSTRACT

Apparatus and methods for protecting a patient from surgical site infection from airborne microbes during surgery. A sterile gas flow conditioning emitter for affixation onto an anatomical surface of a patient adjacent a site of incision is anatomically shape conforming for attaching a unidirectional coherent non-turbulent flow field of sterile gas substantially anatomically levelly on that anatomical surface and flowing the flow field in the direction of that site while essentially preventing ambient airborne particles from entering the interior of the flow field under the emitter to maintain the gas essentially sterile during passage over the site.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

This invention relates to surgery, and more particularly, to airbarriers used to reduce contamination of surgical sites.

2. Background Art

Hospital-acquired infections (“HAI”), also known as nosocomialinfections, are a significant problem in modern healthcare systems. In2002, approximately 1.8 million people contracted an HAI in U.S.healthcare facilities, and approximately 100,000 died as a result. HAIdramatically increases patient length of stay and cost and decreaseshospital bed availability for other patients. The second most prolificcause of HAI is surgical site infections (“SSI”), which account forabout 22% of all nosocomial infections. Hollenbeak C S, et al., Theclinical and economic impact of deep chest surgical site infectionsfollowing coronary artery bypass graft surgery, CHEST, 118 (2) (August2000); National Nosocomial Infections Surveillance (NNIS) System Report,data summary from January 1992 through June 2004, issued October 2004,Centers for Disease Control and Prevention, publ. AMERICAN JOURNAL OFINFECTION CONTROL, 32, 470-85 (2004); Chu VH, et al, Staphylococcusaureus bacteremia in patients with prosthetic devices: costs andoutcomes, THE AMERICAN JOURNAL OF MEDICINE, 118 (12) (December 2005);Klevens N R, et al., Healthcare-associated infections and deaths in U.S.hospitals, 2002, PUBLIC HEALTH REPORTS, 122, 160-166 (March-April 2007).

SSI infections mostly are “staph” infections, caused by the bacteriumStaphylococcus aureus, which occurs harmlessly on human skin andfrequently in the nose. If these bacteria gain access to a normallysterile space, such as in the capsule of a joint, they may multiplywithout resistance and create a huge infectious burden on the host. Theyoften attach to prosthesis surfaces and multiply within denseaggregations called biofilms. Bacteria protected within biofilms aremuch harder to kill than individual isolated bacteria. SSI frombacterial invasion is particularly deleterious in procedures such asorthopedic joint arthroplasty, cardiovascular surgery, and neurosurgery.These types of infections develop deep within the body, are difficult totreat, and are devastating to patients. Antibiotics can't alwayspenetrate tissues to reach bacteria that have taken root on implantedmaterials, and revision surgery on the infected joint is often necessaryto eradicate the infection. Sometimes the infection will have caused somuch bone loss that a second prosthesis replacement isn't an option, inwhich case the only option is fusing the bones together leaving thejoint stiff and immobile and the patient in need of a mobility aid.

Airborne bacteria present in the operating room environment are aleading cause of SSI. A primary vector of microbial intrusion into thesurgery site is direct precipitation from the atmosphere. Bacteria aregenerally 0.5-1 μm in size or larger and have a tendency to clustertogether and attach to other larger particles. Airbornebacteria-carrying particles measure about 4 μm to 20 μm. Humansconstantly shed skin scales in the 5-20 μm particle range into theatmosphere. Most current research regarding the vectors of airbornebacteria into the surgery site is based upon a study performed in 1982,Whyte W. et al., The importance of airborne bacterial contamination ofwounds, JOURNAL OF HOSPITAL INFECTION, Vol. 3(2), 123-135 (June 1982).Whyte estimated that the source of about 98% of the bacteria present ina surgical wound was airborne. Studies indicate that controlling thepresence of bacteria in the operating room atmosphere can reduce therisk of SSI.

Laminar flow operating rooms (“LFOR”) were developed in the 1970's and1980's to reduce the incidence of SSI from airborne bacteria. In a LFOR,clean air is introduced from filters in either the ceiling (verticalflow) or side wall (horizontal flow) at low speeds, e.g., 20 to 40 m/min(66 to 132 ft/min), to preserve laminar flow. The benefit thought to beachieved by LFOR air distribution is that filtered air flowing inlaminar streams does not mix with contaminated air before reaching thesurgery site, thus preventing airborne bacteria from reaching thesurgery site. However, the ability of LFORs to accomplish this andprevent infections is qualified and debatable. Ritter M A, et al., Theoperating room environment as affected by people and the surgical facemask, CLINICAL ORTHOPEDICS, 111, 147-150 (September 1975); Franco J A,et al., Airborne Contamination in Orthopedic Surgery. Evaluation ofLaminar Air Flow System and Aspiration Suit, CLINICAL ORTHOPAEDICS ANDRELATED RESEARCH, Number 122 (January-February, 1977); Ritter M A, etal., Comparison of Horizontal and Vertical Unidirectional (Laminar)Air-flow Systems in Orthopedic Surgery, CLINICAL ORTHOPAEDICS, 129(November-December 1977); Ritter M A, et al., Laminar Air-Flow VersusConventional Air Operating Systems: A Seven-Year Patient Follow-Up,CLINICAL ORTHOPAEDICS, 150 (July-August 1980); Whyte W, et al., Theimportance of airborne bacterial contamination of wounds, Journal ofHospital Infection, 3(2), 123-135 (June 1982); Lidwell O M, et al.,Effect of ultraclean air in operating rooms on deep sepsis in the jointafter total hip or knee replacement: a randomised study, British MedicalJournal, Vol. 285 (July 1982); Lidwell O M, et al., Airbornecontamination of wounds in joint replacement operations: therelationship to sepsis rates, JOURNAL OF HOSPITAL INFECTION, 4 (2),111-131 (June 1983); Horworth F H, Prevention of Airborne Infectionduring Surgery, ASHRAE TRANSACTIONS, 91(1b), 291-304 (1985); Horworth FH, Prevention of Airborne Infections in Operating Rooms, HOSPITALENGINEERING, 40 (8), 7-23 (1986); Charnley, J, A clean-air operatingenclosure, THE CLASSIC, Number 211 (October 1986); Lidwell O M, et al.,Ultraclean air and antibiotics for prevention of postoperativeinfection. A multicenter study of 8,052 joint replacement operations,ACTA ORTHOPAEDICA SCANDINAVICA, 58, 4-13 (1987); Van Griethuysen A J A,Surveillance of wound infections and a new theatre: unexpected lack ofimprovement, JOURNAL OF HOSPITAL INFECTION 34, 99-106 (1996); Ritter MA, Operating room environment, CLINICAL ORTHOPAEDICS & RELATED RESEARCH,369, 103-109 (December 1999); Persson M, et al., Wound ventilation withultraclean air for prevention of direct airborne contamination duringsurgery, INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY, 25 (4) (April2004); Clarke M T, et al., Contamination of primary total hipreplacements in standard and ultra-clean operating theaters detected bythe polymerase chain reaction, ACTA ORTHOPAEDICA 75 (5), 544-548 (2004);Pereira M L, et al., A Review of Air Distribution Patterns in SurgeryRooms under Infection Control Focus, ENGENHARIA THERMICA (ThermalEngineering), 4 (2), 113-121 (October 2005); Miner A L, et al., DeepInfection After Total Knee Replacement: Impact of Laminar AirflowSystems and Body Exhaust Suits in the Modern Operating Room, INFECTIONCONTROL AND HOSPITAL EPIDEMIOLOGY, 28 (2), (February 2007); PasquarellaC, et al., A mobile laminar airflow unit to reduce air bacterialcontamination at surgical area in a conventionally ventilated operatingtheatre, JOURNAL OF HOSPITAL INFECTION, 66 (4), 313-319 (August 2007).

While laminar flow air is clean when leaving the air vents in the wallor ceiling, it must traverse a significant distance in a room laden withcontaminants and will entrain ambient particles in its flow. Overheadlights and staff leaning over the patient are regularly interposedbetween the clean air source and the surgery site, creating a directvector for contaminants to compromise the patient. Recent studies haveshown that the primary source of the airborne contamination in theoperating room, assuming HVAC systems are properly designed andmaintained, is the shedding of bacteria and particulate matter, such asskin scales bearing bacteria, by people present in the operating room,including personnel outside the sterile surgical field (circulatingnurses, anesthesiologists, radiology technicians and other technicians).See e.g., Edmiston Jr. C E, et. al., Molecular epidemiology of microbialcontamination in the operating room environment: Is there a risk forinfection?SURGERY, 138:573-582 (October 2005). In other words, theinclusion of surgical personnel and equipment within the air barrier maylimit the ability of LFOR systems to reduce airborne microbes arisingfrom those people and that equipment. Moreover, laminar flow operatingtheatres are uncommon and costly. Installing one laminar flow surgeryroom costs at least about $500,000, is a major construction project, anddisrupts surgery room availability.

An alternative approach to LFOR systems has been to move a source ofsterile air closer to the patient or the operating table. U.S. Pat.3,820,536 (Anspach Jr. et al., 1974) describe bringing a high efficiencyparticulate air filter (“HEPA”) blower up to an operating table andangling the blown air downwardly onto the patient. In a study, Thore M,et al., Further bacteriological evaluation of the TOUL mobile systemdelivering ultra-clean air over surgical patients and instruments,JOURNAL OF HOSPITAL INFECTION 63, 185-192 (2006), a freestanding mobilelaminar flow clean air source was evaluated, similar to the devicedescribed in U.S. Pat. No. 3,820,536. The device was positionedapproximately 2 m away from the surgery site at an elevation above andangled down toward the site and said to have delivered laminar flow HEPAair toward the surgical field. Since the device could be positionedcloser to the surgery area than would be the case where the air sourceis built into the infrastructure of the room, it was thought that thecontamination effect of room traffic would be reduced. During actualsurgery, Thore et al. found that the device was ineffective after theair traveled further than approximately 1 m from the unit due to theroom dynamics between the air source and the surgery site.

Others that have tried moving the source of sterile air closer to thepatient or the operating table include Meyer as described in U.S. Pat.No. 4,275,719 (1981) and Smets as described in U.S. Pat. No. 4,422,369(1983). Mayer described a pair of nozzles flat in cross section alignedon either side of an incision area (one nozzle to blow sterile air, theother to collect it) with the nozzles held in place with strips of tape.Smets described a system in which a curtain of sterile air is formedabove a surgical table also using aligned blower and suction nozzles. Adrape reaches from the lower edge of the blower nozzle to the surface ofa table to prevent entrainment of ambient air beneath the blower nozzle.This arrangement set up a turbulent circulation under the blower nozzle.A nozzle in the shape of a flattened cone is placed on the surface ofthe table to flow sterile air into the circulation opposite thedirection of flow of the overhead air curtain to neutralize disturbancescaused by the gas curtain.

Other than LFOR's, the only solution finding its way into mainstreamutilization has been body exhaust suits (“BES”), also developed in the70's and 80's. Colloquially called a “space suit,” these consist of aplastic helmet with a built-in filter over which a sterile hood with aview pane is placed to completely encapsulate the surgeon's face andneck. Contaminants from the surgeon's head region are captured andfiltered before the air is exhausted back into the operating room. Theability of BES to prevent contamination of the surgery site is viewed asunproven. Franco J A, et al., CLINICAL ORTHOPAEDICS AND RELATED RESEARCH(1977), ibid; Der Tavitian J, et al., Body-exhaust suit versus occlusiveclothing—a randomized, prospective trial using air and wound bacterialcounts, JOURNAL OF BONE AND JOINT SURGERY (British), 85-B:4, 490-494(2003); Miner A L, et al., INFECTION CONTROL AND HOSPITAL EPIDEMIOLOGY,ibid; Ritter M A, CLINICAL ORTHOPAEDICS & RELATED RESEARCH (2007), ibid.Body exhaust suits isolate the surgeon, not the patient. Moreover,typically, only surgical personnel working in the operating room withinthe surgical field (surgeons, surgical assistants and technicians, andscrub nurses) wear the suits during a surgery.

Beyond the mainstream LFOR and BES solutions, virtually no newtechnology has emerged and been generally adopted over the past 30-plusyears to remove the source or cause of SSI, and even the LFOR and BESapproaches to the SSI problem are rarely used outside of orthopedicjoint replacement surgery because they are so costly and complicated. Asa result, the incidence of SSI remains largely unabated. Innovationscurrently being pursued in research and industry to combat SSI infectionhave shifted primarily from preventive solutions for the operating roomto post operative pharmaceutical solutions, directed to creatingantibacterial drugs that would prevent infections from developingpost-operatively and would mitigate the effects of infection oncemicroorganisms enter the body. History is testament that drug resistantbacteria develop as a result of application of antibacterial drugs.

The root problem remains: how to prevent bacteria shed by personnel inthe operating room from invading the surgical wound during surgery. Asecond part is how to solve the root problem in a way that canfacilitate widespread adoption of the solution and by widespreadadoption significantly combat and reduce SSI. For widespread adoption,the solution must not only be effective, it has to be cost effective,and it should be easy for surgeons and staff to implement. Yet, for morethan 30 years since initial appreciation of the root cause of SSI, anddespite urgent need and serious efforts of many dedicated professionals,scientists and engineers to address the root problem, SSI from operatingroom bacteria remains a serious unresolved health care issue.

The present invention is directed to the root cause of the SSI problem:effectively preventing bacterial invasion of a surgically created woundduring the surgery; and is also directed to the second part of theproblem: making the solution effective, inexpensive and easy toimplement. The invention has particular advantage for surgicalprocedures involving deep, “clean” anatomical structure, for example,without limitation, orthopedic joint arthroplasty, pediatric ventricularshunt implantation, cardiac implant and vascular surgery, andlong-duration procedures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. is a perspective view of apparatus including an embodiment of aflow conditioning gas emitter in accordance with the invention.

FIG. 2 is a perspective view including an exploded view of the flowconditioning gas emitter of FIG. 1.

FIG. 3 is an isometric view of the upper half of the casing of anemitter assembly of FIGS. 1 and 2.

FIG. 4 is an isometric view of the lower half of the casing of theemitter assembly of FIGS. 1 and 2.

FIG. 5 is a top view of an embodiment of an emitter assembly of FIGS. 3and 4 placed on a surface 102, schematically depicting flow lines of agas emitted from the emitter assembly.

FIG. 6 is a side sectional view of an embodiment of an emitter assemblyof FIGS. 3 and 4 placed on surface 102, schematically depicting flowlines of a gas emitted from the emitter assembly.

FIG. 7 is an isometric view of another emitter assembly in accordancewith the invention.

FIG. 8 is a side sectional view of the embodiment of FIG. 7schematically depicting flow lines of a gas emitted from the emitterassembly

FIG. 9 is a graph showing the results of the test of Test Example 1.

FIGS. 10, 11 and 12 are graphs showing the results of the test of TestExample 2

FIGS. 13 and 14 are graphs showing the results of the test of TestExample 3.

FIG. 15 is a graph showing the results of the test of Test Example 4.

FIG. 16 is a graph showing the results of the test of Test Example 5.

FIG. 17 is an isometric depiction of the flow trace elements emergingfrom a prior art emitter and passing over an arcuate surface.

FIG. 18 is a depiction of the flow trace elements in a vertical planethrough the center of the emitter of FIG. 17.

FIG. 19 is a depiction of the flow trace elements at the lateral edge ofthe emitter of FIG. 17.

FIG. 20 is an isometric depiction of the flow trace elements emergingfrom a prior art emitter and passing over a flat surface.

FIG. 21 is a depiction of the flow trace elements in a vertical planethrough the center of the emitter of FIG. 26.

FIG. 22 is a depiction of the flow trace elements at the lateral edge ofthe emitter of FIG. 17.

FIG. 23 is an isometric depiction of the flow trace elements emergingfrom an emitter like emitter assembly of FIGS. 1-4 and passing over anarcuate surface.

FIG. 24 is a depiction of the flow trace elements in a vertical planethrough the center of the emitter of FIG. 23.

FIG. 25 is a depiction of the flow trace elements at the lateral edge ofthe emitter of FIG. 23.

FIG. 26 is an isometric depiction of the flow trace elements emergingfrom an emitter like emitter assembly of FIGS. 23-25 but having athicker barrier.

FIG. 27 is a depiction of the flow trace elements in a vertical planethrough the center of the emitter of FIG. 26.

FIG. 28 is a depiction of the flow trace elements at the lateral edge ofthe emitter of FIG. 26.

FIG. 29 is an isometric depiction of the flow trace elements emergingfrom an emitter like emitter assembly of FIG. 23 having no barrier underthe emitter, and passing over an arcuate surface.

FIG. 30 is a depiction of the flow trace elements in a vertical planethrough the center of the emitter of FIG. 29.

FIG. 31 is a depiction of the flow trace elements at the lateral edge ofthe emitter of FIG. 29.

FIG. 32 is a isometric depiction of the flow trace elements emergingfrom a modified emitter of the type shown in FIG. 20 and passing over anarcuate surface.

FIG. 33 is a depiction of the flow trace elements in a vertical planethrough the center of the emitter of FIG. 32.

FIG. 34 is a depiction of the flow trace elements at the lateral edge ofthe emitter of FIG. 32.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following detailed description of embodiments, reference is madeto the accompanying drawings, which form a part hereof and in which areshown, by way of illustration, specific embodiments in which theinvention may be practiced. Specific details disclosed herein are inevery case a non-limiting embodiment representing concrete ways in whichthe concepts of the invention may be practiced. This serves to teach oneskilled in the art to employ the present invention in virtually anyappropriately detailed system, structure or manner consistent with thoseconcepts. It will be seen that various changes and alternatives to thespecific described embodiments and the details of those embodiments maybe made within the scope of the invention. Because many varying anddifferent embodiments may be made within the scope of the inventiveconcepts herein described and in the specific embodiments hereindetailed without departing from the scope of the present invention, itis to be understood that the details herein are to be interpreted asillustrative and not as limiting.

The various directions such as “upper,” “lower,” “bottom,” “top,”“back,” “front,” “perpendicular”, “vertical”, “horizontal,” “length” andwidth” and so forth used in the detailed description of embodiments aremade only for easier explanation in conjunction with the drawings toexpress the concepts of the invention. The elements in embodiments maybe oriented differently while performing the same function andaccomplishing the same result as obtained with the embodiments hereindetailed, and such terminologies are not to be understood as limitingthe concepts which the embodiments exemplify.

As used herein, the use of the word “a” or “an” when used in conjunctionwith the term “comprising” (or the synonymous “having” or “including”)in the claims and/or the specification may mean “one,” but it is alsoconsistent with the meaning of “one or more,” “at least one,” and “oneor more than one.” In addition, as used herein, the phrase “connectedto” means joined to or placed into communication with, either directlyor through intermediate components.

Private research in which one of us participated found that the numberof airborne particles 10 μm or larger in size present in an operatingroom during actual hip and knee joint arthroplasties conducted undercarefully controlled testing, but without benefit of our invention, wasassociated with the number of bacterial colony forming units (CFU) grownfrom air sampled within the sterile field approximately 40 cm from thesurgical incision at the surgical site during the arthroplasties.(Reference herein to 10 μm particles is to be understood to mean 10 μmand larger.) The number of 10 μm airborne particles was also associatedwith the number of surgical staff present in the operating room. Thefinding that the number of 10 μm particles was correlated with thenumber of CFU at the surgical site supports airborne particulatecontamination of the wound as a source of post-operative infection injoint arthroplasty. When the density of 10 μm particles in theseoperating rooms exceeded 300 particles/ft³ in any 10-min interval, theaverage CFU count at the surgical site exceeded 25 CFU/m³ during thatinterval. It is likely that the correlation of larger particles (10 μmand larger) with CFUs observed in this study was attributable to thelarger particles being capable of carrying bacteria. Thus a device andmethodology that would exclude airborne particles 5 μm and larger fromthe surgical field would help protect the surgical site from bacterialcontamination.

In accordance with the present invention, the embodiments and methodsdescribed herein work to create a figurative “cocoon” of essentiallysterile gas immediately overlaying a surgical opening, sometimes calleda surgical wound, to protect the wound from contamination by ambientairborne particles. The cocoon is a localized flow field of coherentnon-turbulent essentially sterile gas. The word “gas” is used to includemixtures, compounds and elemental gases that are not deleterious forsurgical use, and includes air, mixtures of air with vapors or othergases having a sterilant property, i.e., having active properties thathelp negate viability of microbes, such as hydrogen peroxide or ozone,mixtures of air with vapors that have analgesic properties, and mixturesof air with low concentrations of one or more denser inert gases, suchas nitrogen or argon, to displace ambient air. Air is mostly used as asource gas for scrubbing by a HEPA device to provide a sterile gasbecause it is free of added cost. The term “sterile gas” means gas fromwhich 90% or more of ambient airborne particulates 0.3 μm and largerhave been removed. The term “essentially sterile gas” is used to mean agas containing 90% or less of particles 5 μm and larger than in ambientair in the room where the methods and embodiments are employed.

The “cocoon” of essentially sterile gas is created to be located beneathboth surgical staff (who are usually leaning over the incision) and theoverhanging operating room equipment, with the result that surgicalstaff, operating room equipment and others in the operating room, whoare a source of airborne particles that may carry microbes, arepositioned outside the protective cocoon. As used herein, “microbes”includes bacteria, fungal spores and other microorganisms present in theambient atmosphere in an operating room.

The cocoon is created by taking advantage of boundary layer surfaceeffects. Coanda described an effect in U.S. Pat. No. 2,052,869 (1935),now called the Coanda Effect, which acted on the observation that when astream or sheet of gas is issued at high velocity through an orificeinto an atmosphere of another gas, a suction effect will be induced atthe point of discharge, drawing forward the adjacent gas in theatmosphere. Coanda showed that if flow of adjacent gas were checked onone side of the orifice, the flow emergent from the orifice would bediverted to the side where the check is imposed. In simple terms, theCoanda Effect is that a jet of gas into an atmosphere of another gasattaches to an adjacent wall. According to traditional fluid dynamics,when a fluid (gas or liquid) moves along a solid surface (a wall,without implication of verticality), frictional forces drag along a thinlayer of the fluid adjacent the surface due to the viscosity of thefluid. This thin layer is called the boundary layer. The boundary layergenerally exists in one of two states: laminar, where fluid elementsremain in well-ordered nonintersecting layers, and turbulent, wherefluid elements totally mix. Turbulence develops when the laminar streamfilaments immediately adjacent the surface separate from the surface.The state of the boundary layer, in the absence of disturbinginfluences, is directly related to the speed of the fluid over thesurface and the distance along the surface-first it is laminar, and thenit changes to turbulent as the speed or distance increases. Thisbehavior is described by a parameter known as the Reynolds number (Re),a non-dimensional number equal to the product of the velocity (v) of thefluid moving over the surface, the density (ρ) of the fluid and arepresentational length (l) divided by the fluid viscosity (μ). Thisrelationship is defined by the formula: Re=vρl/μ.

In accordance with the present invention, the cocooned protection of thesurgical site is achieved by attaching a unidirectional coherentnon-turbulent flow field of essentially sterile gas substantiallyanatomically levelly on an anatomical surface of a patient adjacent thesite of a surgical incision, and maintaining that flow fieldsubstantially anatomically levelly along the surface anatomy of thepatient up to and through the incision site while keeping the gasessentially sterile. The flow field sweeps ambient airborne particlesalong the outer layers of the flow field cocoon away from the interiorlayers over the surgical wound. The flow field transitions to turbulentflow past the field of effect disbursing ambient particles away from theoperating table.

In order to accomplish this, there is provided apparatus for affixationonto an anatomical surface adjacent a site of incision typical for atype of surgery to protect a patient from surgical site infection duringthe surgery. The apparatus comprises anatomically shape conforming meansfor attaching a unidirectional coherent non-turbulent flow field ofsterile gas substantially anatomically levelly on said anatomicalsurface flowing in the direction of the incision site and preventingambient airborne particles from entering the interior of the flow fieldunder said means sufficiently to maintain said gas essentially sterileat the incision site. Embodiments of apparatus disclosed herein providethe means for accomplishing the stated protection.

In one embodiment, the apparatus comprises a flow conditioninganatomically shape conforming emitter of a sterile gas for attaching aunidirectional coherent non-turbulent flow field of sterile gassubstantially anatomically levelly on the anatomical surface of apatient flowing in the direction of the site and preventing ambientairborne particles from entering the interior of the flow field underthe emitter to maintain the gas essentially sterile during passage overthe site. In an embodiment, the emitter has an undersurface so matchingthe shape of the anatomical surface that, when the emitter is affixed tothe anatomical surface, ambient airflow is substantially completelyprevented from penetrating underneath the emitter and entering theinterior of the coherent non-turbulent flow field. In an embodiment, theemitter has an outlet for the sterile gas having: a dimension of heightand width, a lower margin essentially uniformly along the outlet widthequidistant to the undersurface, and a dimension of height between theoutlet and the undersurface such that when the emitter is affixed ontothe anatomical surface the gas flow from the outlet is substantiallyanatomically level with the anatomical surface of the patient across thewidth of the outlet. In an embodiment, the mentioned portion isdeformable to provide the mentioned dimension of height.

There is thus enabled and provided a method of performing surgery on apatient comprising making a surgical incision in a portion of apatient's anatomy covered by an attached unidirectional coherentnon-turbulent flow field of essentially sterile gas, the fieldoriginating from a substantially anatomically level position adjacent tothe site of incision under flow conditions providing a boundary layer ofthe flow field attached to the anatomical surface for a distance atleast extending through the surgical site. “Non-turbulent” encompassesboth well-ordered coherent laminar flow and still coherent flowtransitioning from well-ordered flow toward (but not yet in) theturbulent state. An instrument, prosthesis, or surgeon or surgicalassistant's fingers or hand inserted into the flow field cocoon over thesurgical site may divert laminar flow around the inserted member thattransitions through a non-turbulent transitional stage into a turbulentflow regime downstream from the inserted member, but the turbulent flowwill be past the surgical opening. Accordingly, coherent non-turbulentflow is maintained through the site of the surgical incision veryeffectively reducing the presence of airborne particulate and microbesinside the cocoon at the surgical site and concomitantly reducing therisk of surgical site infection.

Forming and maintaining a unidirectional coherent non-turbulent flowfield of essentially sterile gas comprises (i) having a supply ofsterile gas, (ii) forming that gas into a unidirectional coherentnon-turbulent flow field, (iii) placing that sterile flow fieldsubstantially anatomically levelly on an anatomical surface of a patientadjacent the site of a surgical incision, and (iv) flowing the fieldsubstantially anatomically levelly along the surface anatomy of thepatient up to and through that site while keeping essentially sterilethe interior portion of that flow field that will come into contact withthe wound created by the surgical incision. Keeping the gas essentiallysterile involves substantially completely preventing ambient airborneparticles 5 μm or larger from invading the interior of the flow field.Airborne particles 5 μm or larger are substantially completely preventedfrom entering the interior portion of the flow field when the content ofparticles 5 μm and larger in the airflow over the surgical opening is90% or less than in ambient air. While the gas flow field sweeps ambientparticles along its edges preventing their entry into the cocoon fromabove, the embodiments also guard against their infiltration from belowadjacent the surface on which the cocoon of sterile air is attached.

Accordingly, there is provided a method for reducing the risk ofintrusion of ambient airborne bacteria into a surgical incision duringsurgery, comprising: affixing a flow conditioning emitter of aunidirectional coherent non-turbulent flow field of sterile gas onto ananatomical surface adjacent a site of the incision, the emitter havingan undersurface so matching the shape of the anatomical surface that,when the emitter is affixed to the anatomical surface, ambient airflowis substantially completely prevented from penetrating underneath theemitter and entering the interior of the coherent non-turbulent flowfield; supplying sterile gas to the emitter; conditioning the sterilegas into a unidirectional coherent non-turbulent flow field emergentfrom the emitter; attaching that sterile flow field substantiallyanatomically levelly on an anatomical surface of a patient adjacent thesite of a surgical incision; and flowing the attached fieldsubstantially anatomically levelly along the anatomical surface of thepatient in the direction of the incision for a distance at leastimmediately past the incision.

The unidirectional coherent non-turbulent flow field is formed in andflowed from an anatomically shape conforming gas emitter, specifics ofwhich are described below. As will be described below, we employ a hoseleading from a HEPA device to a flow conditioning emitter formed inaccordance with our invention. The hose is constructed of a materialproviding it flexibility and maneuverability allowing the emitter to beplaced substantially anatomically levelly on a portion of a patient'ssurface anatomy adjacent a site on the patient's anatomy where anincision is to be made. Sterile gas received in the emitter from thehose is turbulent, and the emitter must transform that turbulentcondition into a unidirectional coherent non-turbulent flow (thistransformation is what is meant by the term “flow conditioning”). Adiffuser as described in more detail below creates a uniformbackpressure along its internal surface that allows the gas to emergefrom the diffuser of the emitter at a constant velocity along itsexternal surface. Flow rates from the HEPA device are adjusted tomaintain the backpressure created by the diffuser that allows the gas toemerge from the diffuser in unidirectional coherent non-turbulent flowat a selected constant velocity. The velocities mentioned herein are thevelocities of the gas emergent from the diffuser in the emitter.

We use the phrase “substantially anatomically level” in a specific wayin relation to placement and maintenance of the flow conditioned gas.The word “level” has a height attribute. It means the lowest part of theunidirectional coherent non-turbulent sterile gas flow field is not somuch higher than the anatomical surface that the lowest part of theemitted sterile gas flow field does not attach to and form a boundarylayer on the anatomical surface adjacent the emitter. In addition theword “level” does not refer to the horizon parallel to an operatingtable; it refers to the direction of flow being generally horizontalwith the anatomical surface of a patient adjacent the site where thesurgical opening will be created. (That surface may or may not be at anangle to the horizon during the surgery, and indeed the anatomy on whichthat surface resides may be moved from one position to another duringsurgery; for non-limiting example, during a knee or hip replacement witha prosthesis, the anatomical surface may be on the thigh, which may ormay not be horizontal with the operating table, and the thigh may bemoved during surgery to manipulate the joint.) The words “anatomicallylevel” or “anatomically levelly” also imply a contour or profileattribute. The relevant ultimate contour is a contour of an anatomicalsurface transverse to the direction of flow of the coherentnon-turbulent gas field, and the relevant controlling contour is thecontour of the orifice of the emitter, which in accordance with theinvention, is a contour designed to conform generally to an anatomicalsurface contour where the emitter ultimately will be placed. Thus“anatomically level” means the flow is level (as defined above) in thedirection of flow for the width of the orifice of the gas emitter fromwhich the flow field emerges. “Substantially” as a modifier of“anatomically level” means that if not exactly anatomically level, theanatomically level placement is close enough to horizontal and closeenough to the anatomical surface to achieve attachment of a boundarylayer of unidirectional coherent non-turbulent flow of sterile gastoward the surgical site along substantially the contour width of theemitter.

The term “anatomical surface” is used in reference to a surface adjacentwhere a surgical incision is to be made. In surgical procedures, thesite of an incision is typically prepared first by painting the surgicalarea with an iodine or other bactericidal solution, followed by layingover the area a film the underside of which is coated with an adhesiveand bactericide, and then by placing over the film a disposable drapehaving a window for the incision work and next by adhering the drape tothe film by an adhesive on the underside borders of the window. Onceprepared, an incision is made within the window through the film intothe painted skin. When we speak about placing an anatomically shapeconforming emitter on an “anatomical surface” adjacent to where anincision is to be made, we do not imply that the emitter is necessarilyapplied directly to the skin; rather we mean the anatomical surface tobe a surface adjacent where an incision is to be made that generallyconforms to the shape of the anatomy adjacent where an incision is to bemade. Accordingly, the emitter may be placed on the skin or on filmadhered to the skin within the drape window or even on the surface ofthe drape adjacent the window where the drape is adhered to the film,provided the emitter is substantially anatomically levelly placed onthat surface. By adjacent to where an incision is to be made, we meanthat the emitter is placed close enough to the site of the incision forthe flow field established in accordance with the invention to reachthrough the site of the incision.

The critical Reynolds number at which gas flow becomes turbulent forflow over a theoretical flat plate (wall) is generally 1×10⁵ (100,000).In the methods and embodiments of this invention, the anatomical surfaceof the patient supplies the wall, albeit not a flat plate. As explainedabove, the operative variables for calculation of a Reynolds number topredict the character of flow are distance and velocity of the gas(density and viscosity of the gas are normally givens). Thus, distancefrom gas emitter to the site for incision is a factor in maintaining theflow field unidirectional, coherent and non-turbulent. The field ofeffect of the essentially sterile coherent non-turbulent flow streamneed not be long, and in an embodiment is approximately half a meterlong or less. Most human anatomies do not have portions for incisionmore distant than a half meter from any anatomical surface where anemitter embodiment could be placed, for example, the distance along thethigh from hip to knee will not exceed about half a meter (about 20inches) except in the very tallest people. Thus spacing of the emitterfrom the site of incision ordinarily will be less than 20 inches,suitably 12 inches or less, for example, 6 inches or even 3 inches. At aspacing of 6 inches separating the emitter from the site of incision,the characteristic of flow over a flat plate predicted using the formulafor calculation of Reynolds number should be coherent and non-turbulentfor velocities of about 800 ft/min (Re=40,500), but at that velocitywould be turbulent (Re=121,700) at a spacing of 18 inches. At a spacingof 18 inches, flow may be coherent and non-turbulent under idealconditions for velocities theoretically of 400 ft/min (Re=60,800) to 500ft/sec (Re=75,100). However, these are theoretical conditions; theactual anatomical surface is not a flat plate and may have some slightwaviness or surface roughness or both. At 6 inches from an emitterflowing air unidirectionally at a velocity of 350 ft/min (5.83 ft/sec)parallel to a flat plate, the Reynolds number is Re=17,700 and will beexpectably fully laminar applied to the anatomical surface of a patient.A relatively moderate flow velocity maintained substantially constant ina range from about 1 m/sec to about 2 m/sec, suitably from about 180ft/min to about 400 ft/min, provides satisfactory results, and may beslower or faster according to the particular emitter and the particularapplication keeping in mind the principles explained herein.

Accordingly, in an embodiment of the invention, there is provided amethod of protecting a patient from surgical site infection of anincision during surgery, comprising conditioning a supply of sterile gasinto a unidirectional coherent non-turbulent flow field, attaching thatsterile flow field substantially anatomically levelly on an anatomicalsurface of a patient adjacent the site of a surgical incision andflowing the attached field substantially anatomically levelly along theanatomical surface of the patient in the direction of the incision for adistance at least immediately past the incision while restrictingambient airborne particles from entering the interior of the flow fieldthat comes into contact with the incision.

In an embodiment, flow conditions are used that cause the flow field toseparate from the anatomy of the patient and become turbulentapproximately half a meter (approximately 20 inches) from the emitter.With this, ambient particles 0.5 μm and larger including any carryingmicrobes are intercepted and swept along the peripheries of the flowcocoon until past the approximately half meter distance from theemitter, where, as the field of flow transitions to a turbulent flowregime, the particles are dispersed by the turbulence away from theoperating table and away from sterilized equipment downstream from thesurgical site rather than remaining in a coherent flow passing down thetable over sterilized equipment which the particles might contaminate.Theoretically (flat smooth surface), for an emitter gas velocity of 400ft/min (6.67 ft/sec), at 24 inches from the emitter, the Reynoldsnumber=81,100 at which flow is likely transitioning toward turbulence.Thus in use on a patient about half a meter is a reasonableapproximation and is borne out by the experimental data described below.

In an embodiment, a supply of sterile gas is conditioned into aunidirectional coherent non-turbulent flow field having a velocity inthe range from about 180 to 400 ft/min and flowed at a rate of fromabout 10 ft³/min to 50 ft³/min, suitably from about 15 ft³/min to about45 ft³/min, and in a particular embodiment, from about 20 ft³/min toabout 43 ft³/min in a flow field extending a distance in the range offrom about 3 inches to about 20 inches.

An anatomically shape conforming emitter is used to perform thefunctions of (a) forming a unidirectional coherent non-turbulent flowfield of sterile gas, (b) placing that flow field substantiallyanatomically levelly onto an anatomical surface, and (c) restrictingambient airflow from infiltrating the interior of the flow field andpotentially contaminating the originally sterile gas that will come intocontact with the surgical wound. An anatomically shape conformingemitter is one that has (a) a flow orifice or outlet the lower margin orboundary of which is essentially uniformly along its width equidistantto the undersurface of the emitter coming into contact with theanatomical surface where the emitter body is to be placed, (b) anundersurface so matching the shape of the anatomy where the emitter bodyis to be placed that ambient airflow is substantially completelyprevented from penetrating underneath the emitter and entering theinterior of the coherent non-turbulent flow emergent from the emitteroutlet, and (c) a portion under the outlet of such height when appliedand attached to an anatomical surface that flow emergent from the outletimmediately above that portion is substantially anatomically level withthe anatomical surface of the patient across the width of the outlet.The height of the portion under the outlet may be adjustable, forexample, that portion may comprise a deformable material that compresseswhen the emitter is applied and attached to the anatomical surface sothat the height of that portion of the emitter does not exceed a heightthat would interfere with the emitter being substantially anatomicallylevel with the relevant anatomical surface of the patient.

The anatomically shape conforming property for the emitter may besupplied, as in the embodiments described in detail below, with acombination of (a) a preformed rigid molded emitter body that generallyconforms to a typical shape of an anatomical surface where the emitteris most likely to be placed for a particular type of surgery, and (b) ashape conformable material affixed to the underside of the molded bodyto provide a barrier substantially completely preventing infiltration ofambient airflow underneath the emitter. The shape conformable materialis sufficiently adaptive to the specific shape and size of theanatomical surface of the particular patient where the generally shapedemitter is placed when the emitter body is affixed to the anatomicalsurface that ambient airflow is substantially completely prevented frompenetrating underneath the emitter and entering the interior of thecoherent non-turbulent flow over the surgical opening. Ambient airflowfrom underneath the emitter is determined to be substantially completelyprevented when the content of particles 5 μm and larger in the airflowover the surgical opening is 90% or less than in ambient air.

Alternatively to forming a rigid molded emitter body, an anatomicallyshape conforming emitter may be manufactured of a pliable or malleablematerial, for example, a synthetic plastic silicone, that is shaped atthe time of a surgery to specifically adapt to the particular surfacecontour of a patient where the emitter is to be placed yet maintain aflow outlet essentially uniformly along its width equidistant to theundersurface of the emitter coming into contact with the anatomicalsurface where the emitter body is to be placed. Other alternativesgiving tangible form to the concepts of the invention may be formed withflexible fabric or plastic enclosures having an inlet and having anemitter outlet maintained to predetermined shape by stiffeners. Thesealternatives would comply with the concepts of our invention so long asthey are capable of providing the unidirectional coherent non-turbulentflow conditions and substantially anatomical level flow field placement,and substantially completely preventing ambient air from penetratingbeneath the emitter when applied to the anatomical surface of thepatient, such as by using a barrier-forming adhesive or a supplementalshape conformable material affixed to the emitter underside.

Having now explained the concepts of our invention and in general how toapply them with an anatomical shape conforming emitter, we now describein detail specific embodiments of anatomical shape conforming emittersthat employ these concepts.

Referring in a first particular to FIG. 1, numeral 10 indicates oneembodiment of the invention for use with a source 11 of sterile air.Apparatus 10 when connected to the source 11 of sterile gas establishesa three-dimensional flow field of substantially coherent non-turbulentflow of sterile gas layering a site on a patient's anatomy where apredetermined surgery is to be performed, to protect the site fromambient airborne particles during the surgery. Apparatus 10 comprises ahose 12 for attachment distally, at connector 13, to a high efficiencyparticulate air filter (“HEPA”) source 11 capable of removing at least90% of air borne particulates 0.3 micrometers and larger in diameter,and proximately, at connector 14, to an anatomically shape conformingemitter assembly 15. Hose 12 is constructed and formed of a materialproviding it flexibility allowing emitter assembly 15 to be placedsubstantially anatomically levelly directly on a portion of a patient'ssurface anatomy 102 adjacent a site on the patient's anatomy. Thisplacement in concert with properly maintained flow conditions causes thesurface of the patient to form the wall or base of a flow field forcoherent non-turbulent sterile gas in which the boundary layer of theflow field can adhere to the surface of the patient.

Emitter assembly 15 comprises a housing 28 having an inlet 33 and anoutlet 41 and enclosing a chamber 29. In the embodiment, the distancebetween the outlet of the housing and the surface of the body anatomy isminimized along the entire width of the outlet of the housing. Toaccomplish this, the physical shape of the housing is designed to matchthe anatomy specific to the surgery. For example, in hip replacementsurgery, the anatomy of the patient at and near the hip is approximatelya cylinder. Therefore, as in the embodiment of the emitter assembly ofFIGS. 1-4 and 7-8, the lower part of the housing has an incurvate shapeto minimize the distance from outlet 41 to the anatomical surface 102across the entire width of outlet 41.

The depicted embodiments including the simulated embodiments used in thecomputer simulations all have an incurvate undersurface, as is suitablefor application of the emitter to a hip or on a leg or other roundportion of the anatomy. However, an emitter providing the functions of(a) forming a unidirectional coherent non-turbulent flow field ofsterile gas, (b) placing that flow field substantially anatomicallylevelly onto an anatomical surface, and (c) restricting ambient airflowfrom getting into the interior of the flow field and potentiallycontaminating the originally sterile gas, can also be used where theanatomical surface has only a slight outward curvature, at least in alean person, such as on the abdomen or chest, and for an double bowedanatomical surface, such as transversely to the spine across the back, adouble bow shaped outlet would be used. The outlet is wide and tallenough to produce a flow field that effectively encompasses the site ofthe incision.

Referring to the embodiments of FIGS. 1-4, housing 28 comprises an upperhousing half 16 as best seen in FIG. 3 and a lower housing half 17 asbest seen in FIG. 4. Upper housing half 16 has an exterior surface 24and interior surface 25, and lower housing half 17 has an exteriorsurface 26 and interior surface 27. Upper housing half 16 is joined tolower housing half 17 to form a housing 28 enclosing chamber 29. In anembodiment, upper housing half 16 widens laterally outwardly from anarrow neck portion 18 to a wide portion 20 that terminates in uppermouth portion 22, and lower housing half 17 widens laterally outwardlyfrom a narrow neck portion 19 to a wide portion 21 that terminates inlower mouth portion 23. The wide portion 20 of upper housing half 16 isgenerally outwardly curving or convex both in exterior surface 24 andinterior surface 25. The wide portion 21 of lower housing half 17 isgenerally incurvate or inwardly curving both in exterior surface 26 andinterior surface 27. The incurvate lower surface 26 of the embodimentdepicted is used where the emitter is to be placed on a generallycylindrical or curvate anatomical surface such as a limb adjacent wherejoint surgery is to be performed. The incurvate shape given outlet 41allows outlet 41 to be located close to an anatomical curvate surfacealong the entire length of the outlet, as depicted in FIG. 4.

In the embodiment depicted in FIGS. 3 and 4, flow guides are providedinside emitter assembly 15 between inlet 33 and outlet 41, placed fordistributing sterile gas across the surface area of flow conditioningmedia. In an embodiment, upper housing half 16 has a pair of baffles 30,31 angled obtusely to one another and spaced apart in front of the upperhalf 32 of a cylindrical inlet 33 into the chamber 29 formed when upperand lower housing halves 16 and 17 are joined. Similarly, lower housinghalf 17 has a pair of baffles 34, 35 angled obtusely to one another andspaced apart in front of the lower half 36 of cylindrical inlet 33. Thebottom edges 37, 38 of upper baffles 30, 31 engage the top edges 39, 40of lower baffles 34, 35 when upper and lower housing halves 16 and 17are joined, to form diverging flow guides 64 (30+34) and 66 (31+35).Upper and lower cylindrical halves, respectively 32 and 36, engage oneanother to form cylindrical inlet 33, and upper and lower mouthportions, respectively 22 and 23, engage to form outlet 41, when upperand lower housing halves 16 and 17 are joined. Sterile gas enteringchamber 29 through inlet 33 is partially admitted straight ahead througha gap 42, 43 between the spaced apart baffle units 64 and 65 and ispartially diverted by flow guides 64, 65 laterally outwardly from thecentral portions of chamber 29.

Upper and lower mouth or outlet portions, respectively 22, 23, terminatein boundary edges, respectively 44, 45, between their exterior surfaces,respectively 24, 26, and their interior surfaces, respectively 25, 27.Between baffles 30, 31 and mouth portion 22 in upper housing half 16 isa raised ridge 46 spanning the width of upper housing half 16.Similarly, between baffles 34, 35 and mouth portion 23 in lower housinghalf 17 is a raised ridge 47 spanning the width of lower housing half16. The portion of upper housing half 16 between lip 44 and ridge 46 isan upper land 48. The portion of lower housing half 17 between lip 45and ridge 47 is a lower land 49. On joinder of upper and lower housinghalves 16, 17, upper and lower lands 48, 49 lodge a diffuser (FIGS. 1-2,see also FIGS. 7-8) comprising a porous media 50 within chamber 29proximate outlet 41 through which sterile gas received in inlet 33 ispassed. The purpose of porous media 50 is to ensure that the air exitingoutlet 41 is all traveling in the same direction (unidirectional) at thesame speed to provide coherent flow from outlet 41 free of turbulence.The media creates a uniform backpressure along its internal surface thatallows the air to emerge at a constant velocity along its externalsurface. Porous media 50 is shaped to fit within and fully occupy thespace in the chamber demarked by the upper and lower lands 48, 49 andsuitably is a foam diffuser media in the range from 70 to 100 ppi (poresper linear inch), for example 80 ppi, foam filter media at a thicknessfitting in lands 48, 49, for example, about 1 inch thick. Alternatively,a finely porous diffuser screen or panel known in the art to produceclosely layered laminar flow may be used.

Referring to FIG. 3, upper housing 16 is provided with a pair of slottedoutlet ears 51, 52 on opposite lateral sides of the housing proximateoutlet 41, and is also provided with a pair of slotted inlet ears 53, 54on opposite lateral sides of the housing proximate inlet 33. Theexterior surface of cylindrical inlet half 32 of upper housing half 16is formed with a recessed land 55 the distal rim 56 of which tapersdistally to form a barb half 57. Similarly, the exterior surface ofcylindrical inlet half 36 of lower housing half 17 is formed with arecessed land 58 the distal rim 59 of which tapers distally to form abarb half 60. Joinder of upper housing half 16 to lower housing half 16provides a circular barb connection 14 for connecting hose 12 to inlet33.

Referring to FIGS. 1, 2, 6 and 7, a shape conforming barrier 61 is incontinuous contact with the lower exterior surface 26 of lower housinghalf 17 along the width of lower mouth 23 and, perforce, outlet 41, forshape conforming placement of the assembly directly on a portion 102 ofthe anatomy of a surgical patient adjacent the incision site. “Shapeconforming” means that the barrier 61 under the generally shapedincurvate lower housing half 17 accommodates to the size of the specificshape of the anatomical portion of a particular patient, in the rangefrom slim to obese, on which the generally anatomically conformingemitter housing is placed. In an embodiment, the shape conformingbarrier is a pad. A conformable pad accommodates various sizes for thesame general anatomical shape, prevents particle entrainment of air andparticles from underneath the housing 28, and assists in minimizing thedistance between the incurvate outlet 41 and the patient. Thisestablishes flow adhering to the surface anatomy of the patient acrossthe site of incision to avoid separation of flow from that surface.

An embodiment of a shape conforming barrier 61 may be a pad ofself-conforming material. An example of a self-conforming material is athree-fourths inch thick white ether foam shaped to correspond (FIG. 2)to the shape underside 26 of emitter assembly 15. A pressure sensitiveadhesive (“PSA”) backing is applied on one side allowing the assemblerto peel off a liner to reveal a sticky backing for adhering the foammaterial to the underside 26 of assembly 15. Self conforming material iscompressible but may take a permanent set once deformed to conform tothe anatomical surface of the patient, or may be resilient afterdeformation. An advantage of resilient self-conforming material is thatthe surgeon may move or shift the emitter during surgery and a resilientself-conforming material will maintain the barrier at the new placement.

Emitter assembly 15 is placed substantially anatomically levelly on thesurface of anatomical portion 102 and secured to the anatomicallyportion to maintain a substantially anatomically level orientation ofoutlet 41 relative to the surface at the site of the anatomy where thesurgery is to occur. Referring to FIGS. 5 and 6, emitter assembly 15 isconformingly applied substantially anatomically levelly to an anatomicalsurface 102 adjacent surgical site 70. Sterile gas from hose 12 ispassed through diffuser 50 of emitter assembly 15 at flow conditionsthat provide a coherent non-turbulent flow 71 which is adherent at aboundary layer 72 to anatomical surface 102. Barrier 61 prevents ambientair and air particles from being entrained in the flow from underneathemitter assembly 15. The conforming substantially anatomically levelapplication of fluid conditioner assembly 15 creates a flow profilesimilar to a fluid flowing over a flat surface. As coherentnon-turbulent flow moves over the surface 102 in a direction indicatedby the flow arrows, viscous forces acting on boundary layer 71 hinderthe flow of the adherent boundary layer relative to the higher layers,and the higher layers move at a higher velocity than the lower andboundary layers. Eventually this will cause transition from a coherentnon-turbulent flow to a turbulent flow that will separate the boundarylayer 71 from surface 102 and cause the flow no longer to adhere tosurface 102. Placement of emitter assembly 15 must not be so distantfrom surgical site 72 as to cause the surgery to be outside theprotective layer of sterile coherent non-turbulent gas flowed fromemitter assembly 15. Depending on the flow conditions selected, emitterassembly is suitably placed within 3 to 12 inches from the surgery site.Flow conditions for providing a coherent non-turbulent flow from emitterassembly 15 include a relatively moderate flow velocity maintainedsubstantially constant in a range from about 180 to 400 ft/min. In anembodiment, the dimensions of a flow outlet of an emitter suitably isabout 8 inches wide and about a 1.9 inches high for a cross sectionalarea of 0.108 ft² giving a flow rate of from 19.4 ft³/min to 43.2ft³/min at a flow velocity of from 180 to 400 ft/min.

At least one releasable fastener is employed for releasably securingemitter assembly 15 to the anatomical portion 102 substantiallyanatomically levelly in shape conforming contact therewith. In anembodiment, a PSA backing may be applied to both sides of the selfconforming material, one backing being used to adhere the material tothe underside 26 of assembly 15, and the other backing may be used toadhere the self conforming material to the anatomical portion 102 or aprotective sterilized film adhered to anatomical surface 102, in eithercase, substantially anatomically levelly and in shape conforming contacttherewith (FIGS. 5-6). The adhesive is releasable, allowing the assemblyto be positioned and repositioned during the course of a surgicalprocedure.

FIGS. 1-3 illustrate an embodiment especially suited to arthroplastysurgeries, such as hip or knee joint replacement. In this embodiment,the releasable fastener comprises at least one mounting strap and strapfastener affixed to the emitter assembly. In the embodiments of FIGS.1-3, a male clip end 62 of a strap 63 inserted through slotted ear 51,passed across the exterior surface 24 of upper housing half 16, andinserted though slotted ear 52, is positioned to be passed around ananatomical limb, for example, an upper thigh in the case of hip or kneesurgery, and inserted into a female clasp end 66 of the fastener, whichis fitted with a release for releasing the male clip end 62. A similarstrap arrangement is provided at the inlet end of emitter assembly 15. Amale clip end (not seen) of a strap 68 inserted through slotted ear 53,passed across the exterior surface 24 of the neck portion 18 of uppercylindrical half 32, and inserted though slotted ear 54, is positionedto be passed around the anatomical limb and inserted into a female claspend 69 of the fastener, which is fitted with a release for releasing themale end. Although mounting straps and fasteners have been depicted, anymanner of releasable fastening may be used, such as any button, clasp,strap, tie, buckle, zipper, catch, snap, or hook and eye fastener.Placement of the mounting straps at the front and the back of the flowconditioning assembly allows the surgeon to strap the assembly firmly inplace. By providing two straps, the assembly can be strapped downevenly, making the outlet flow approximately parallel, and in the caseof the incurvate shape tangent, to the patient. Also, the distancebetween the bottom of the outlet 41 and the patient is further minimizedwhen the straps are tightened, compressing the conformable pad.

In use of the embodiment of FIGS. 1-6, the risk of intrusion of ambientairborne bacteria into a surgery site during surgery is reduced byproviding a emitter assembly, such as emitter assembly 15, for directplacement on a portion 102 of a patient's surface anatomy immediatelyadjacent the surgery site, substantially anatomically level with theanatomical portion 102. Emitter assembly 15 has upper and lower exteriorsurfaces 24, 26, a chamber 29 within such exterior surfaces, chamber 29having an inlet 33 adapted to receive sterile gas from hose 12 and anoutlet 41 spaced from inlet 33, outlet 41 having a height and widthpredetermined to establish a height and width of a protective envelope,and porous media 50 within chamber 29 proximate outlet 41 through whichsterile gas received in inlet 33 is passed to provide coherentnon-turbulent flow from outlet 41. Shape conforming barrier 61 incontinuous contact with lower exterior surface 26 of emitter assembly 15along the width of outlet 41 provides for shape conforming placement ofassembly 15 directly on anatomical portion 102 adjacent the surgicalsite to prevent entrance of ambient gas between the lower exteriorsurface 26 of assembly 15 and anatomical portion 102. A high efficiencyparticulate air filter source 11 of sterile gas to inlet 33 is provided.Emitter assembly 15 is secured to anatomical portion 102 immediatelyadjacent to the surgical site with outlet 41 facing the sitesubstantially anatomically level with anatomical portion 102 and withbarrier 61 in shape conforming contact with anatomical portion 102 toprevent entrance of ambient gas between lower exterior surface 26 andanatomical portion 102. Sterile gas is caused to flow from source 11through inlet 33 into chamber 29, thence through porous media 50 toprovide flow coherence, and thence out outlet 41, at a velocitysufficient to form over the surgical site a flow cocoon or envelope 80of substantially coherent non-turbulent sterile gas having upper flowboundaries 81, lower flow boundaries 82 and lateral flow boundaries 83shaped by outlet 41. The lower boundaries 81 maintain a boundary layer84 adjacent the anatomical surface 102 of the patient at least to thesurgical site 101 and potentially at least to 0.5 meters distant fromthe emitter outlet. Lateral boundaries 83 are wider than the surgicalsite, and upper boundaries 81 have velocities effective to entrainambient particles impinging on the upper boundaries 81 and sweep thempast surgical site 101. In an application of this method, the sterilegas passes from the outlet at a velocity from about 55 to about 122m/min (about 180 to about 400 ft/min). The sterile gas source 11 is ahigh efficiency particulate air filter source capable of removing atleast 90% of air borne particulates 0.3 micrometers and larger indiameter.

Another embodiment is illustrated in FIG. 7. In this embodiment likeelements as for the embodiment of FIGS. 1-6 carry the same referencenumerals and need no further description. Although not shown in FIG. 7to avoid obscuring other details, it is to be understood that internalbaffles are present in the embodiment of FIG. 7 as in the embodiment ofFIG. 1-6. The upper housing half 75 of emitter assembly 76 of FIG. 7additionally comprises a raised flat surface 77 on at least a portion ofthe upper external surface 24 of emitter assembly 76, surface 77providing a tray useful for placement of surgical instruments. The traysurface suitably supports a rubber or other polymeric friction pad (notshown) providing a high grip surface for the instruments. Between traysurface 77 and upper neck portion 18, upper housing half 75 also has anelevated roof portion 78 that opens in an upper outlet 79 from theinterior of emitter assembly 76. Outlet 79 faces and opens onto tray 75for passing sterile gas across tray 75 to maintain a sterile field onthe tray for sterile instruments. As indicated by FIG. 8, the sterilegas flow across tray 77 not only sweeps away any ambient airbornemicrobes that might otherwise fall onto the instruments, but also passesover the top of the sterile gas flow field emerging from outlet 41 forsweeping any microbes that might be on the instruments if theinstruments become non-sterile from usage or if non-sterile when firstplaced on the tray. There is no flow diffuser such as flow diffuser 50to condition the sterile gas emerging from upper outlet 79 and while thegas emerging from upper outlet 79 is sterile, passage of the gas overinstruments placed in the path of the emergent gas can transition thegas into a turbulent flow, and this is useful, in that any airbornemicrobes swept from the sterile area over tray 77 are disbursed by theturbulence out away from the operating table while all the time thecocoon zone created by sterile coherent non-turbulent gas emerging fromlower outlet 32 protects the surgical site from those and other airbornemicrobes,

Thus there is also provided a method of maintaining sterile surgicalinstruments sterile, comprising placing the instruments on a tray 77located on at least a portion of an upper surface of a emitter assembly76 comprising upper and lower exterior surfaces 15, 17 and a chamber 28within the exterior surfaces that has an inlet 24 adapted to receivesterile gas from a source, such as through hose 12, and also has aplurality of outlets each spaced from inlet 24 and vertically spacedfrom one another, a lower outlet 32 having a height and widthpredetermined to establish a height and width of a cocooning zone, andan upper outlet 79 facing and opening across tray 77. Sterile gasreceived in inlet 24 is passed through porous media 41 within chamber 28proximate lower outlet 24 to provide coherent non-turbulent flow fromlower outlet 32. A shape conforming barrier 52 is in continuous contactwith lower exterior surface 17 along the width of lower outlet 32 forshape conforming placement of assembly 76 directly on a portion ofanatomy of a patient adjacent a site for surgical incision in thepatient to prevent entrance of ambient gas between lower exteriorsurface 17 and the portion of anatomy on which the assembly 76 isplaced. Sterile gas is flowed over tray 77 from upper outlet 79 while aunidirectional coherent non-turbulent flow field of sterile gas isflowed from lower outlet 32 substantially anatomically levelly along andattached to the anatomical surface of a surgical patient toward theincision site from a position adjacent the incision site. The sterilegas from outlet 32 passes along the anatomy to the incision site underflow conditions sufficient to maintain a boundary layer of the flowfield attached to the anatomical surface for a distance extending atleast through the surgical site, while entrainment of ambient particlesunder the flow field is prevented by barrier 61.

Use of the flow conditioning assembly embodiments described in FIGS. 1-4was tested for its ability to provide a three dimensional zone ofsubstantially coherent non-turbulent gaseous flow layering a site suchas one where a surgery would be performed, to protect the site fromintrusion of ambient airborne particles during the surgery. The testsare described in Test Examples 1-5.

Test Example 1 Particulate Reduction

A map of the particulate reductions for X (width) and Y (length)locations was generated using a test fixture. A device system inaccordance with the embodiment 10 depicted in FIG. 1 (in this andsubsequent examples called the “device”) was used to create a clean airenvelope on a test surface. Particulate count readings within the cleanair envelope at discrete locations were compared to the ambient levelsso a percent reduction could be computed. Data was taken over a gridspanning 7.5″ wide and 24.35″ long, with data taken every 0.75″ in the Xdirection and 3″ in the Y direction. A stainless steel tube was used asa probe to sample at various locations while having a minimum impact onthe performance of the system. Sterile air was flowed through the deviceat about 4 ft/sec at a flow rate of about 0.24 ft³/sec. FIG. 9 is agraph of the results, with the device blowing sterile air in theY-direction, toward the 23.35″ mark. Measuring reduction of particulatesin sizes 5 μm and greater, reference numerals indicate percent ofreduction as follows:

Reference Percent numeral reduction 500  90-100 510 80-90 520 70-80 53060-70 540 50-60 550 40-50 560 30-40 570 20-30

The results show that the device is capable of reducing particulates insizes 5 μm and greater by 90-100% over an area greater than 5″ wide by20″ long. (The reading on the particle counter at 10 μm is all particles10 μm and greater).

Test Example 2 Substantially Anatomically Level Flow

In the embodiments depicted above in which the exterior lower surface ofemitter assembly 15 is incurvate, the adherence of flow to theanatomical surface is on a curvate anatomical surface, not a flatsurface. The ability of the device to create an envelope of clean airalong a curved portion of anatomy was examined by mounting the deviceonto a convex cylindrical surface with a radius of curvature of 8″ and alength of 27″. These dimensions were chosen to approximate thedimensions of a human thigh. Cross-sectional maps of the particulatereductions in the X (width)-Z (height) plane were generated by takingmeasurements, using the methodologies and performance settings ofExample 1, along the length of the cylindrical surface. FIGS. 10, 11 and12 show the particle reduction efficiencies, respectively, at Ydistances of 0.35″, 6.35″, and 12.35″ away from the device air emitter.Measuring reduction of particulates in sizes 5 μm and greater, referencenumerals indicate percent of reduction as follows

Reference Percent numeral reduction 600  90-100 610 80-90 620 70-80 63060-70 640 50-60 650 40-50 660 30-40 670 20-30 680 10-20 690  0-10

The maps indicate that the clean air zone adheres and conforms to thecurved test surface.

Test Example 3 Bacterial Reduction Ambient Air

Numerous 10 cm diameter settle plates (tryptic soy agar with 5% sheep'sblood) were exposed over a 24″ wide by 48″ long surface to ambient airconditions. The device outlet was placed adjacent to the surface toexamine its area of effect. The plates, which are 1.5 cm tall, were setonto a flat surface in order to mimic the potential effect of physicalstructures to disrupt the coherent non-turbulent flow field. During acontrol set of trials, 10 settle plates were exposed to ambient air for30 minutes with the device in place but not activated (“Device OFF”).During an experimental set of trials, 45 plates were exposed to ambientair for 30 minutes with the device activated (“Device ON”). For settleplates exposed during the Device OFF control runs, the mean bacterialcolony forming unit (“CFU”) count was 5.65, standard deviation of 1.63(FIG. 13). For the experiment group (Device ON), the mean CFU count onplates exposed during the experiment runs was 1.69, standard deviationof 1.24, with the bacteria populations heavily weighted to areas outsidethe width of the device and furthest away (FIG. 14). An areaapproximately 6″ wide and 17″ long directly proximate to the outlet ofthe device showed near-zero CFU readings. A typical incision during hiparthroplasty, which is approximately 5 inches square or smaller, wouldfit within the boundary area. These data also indicate that the devicedoes not concentrate airborne bacteria and redistribute them downstreamfrom the device, which could be an issue if sterile equipment such assurgical implants and instrumentation were placed in that area.

Test Example 4 Bacterial Reduction Challenge

Challenge test trials were conducted during which a high concentrationof airborne bacteria, representing approximately 24 times the normallevel of ambient airborne bacteria, was introduced over an areaapproximately 10″ wide by 27″ long that was being protected by thedevice. Thirty-five (35) settle plates (65 mm diameter, tryptic soyagar, 5% sheep's blood) were evenly spaced throughout the test surfaceand were exposed to the challenge conditions for 10 minutes during eachtrial. Measuring reduction of particulates in sizes 5 μm and greater,reference numerals indicate percent of reduction as follows:

Reference Percent numeral reduction 700  90-100 710 80-90 720 70-80 73060-70 740 50-60 750 40-50 760 30-40 770 20-30 780 10-20

The plate CFU counts demonstrated, as shown in FIG. 15, that the deviceis capable of reducing the presence of airborne microorganisms by morethan 90% in an area greater than approximately 6″ wide and 10″ longduring these extreme conditions.

Test Example 5 Simulated Surgeries Particulate Counts

Several total hip arthroplasty surgeries were conducted at an orthopedichospital on fresh frozen (i.e., not embalmed) cadavers to determine theefficacy of the device when deployed under surgical conditions. Thesurgeries were conducted using the standard methods, personnel,instruments, and techniques performed by the surgeon except thatprosthetic components were not implanted and no anesthesia wasadministered. All other sterile preparation, instruments, incisions, andmethods were representative of an actual surgical procedure. Airbornemicrobes and particulates were captured through 130 cm lengths ofsterile tubing at two locations: within 5 cm of the surgical site underthe air envelope provided by the embodiment of FIGS. 1-4 (“Test”) and ata location within the sterile field but not under the air envelope(“Control”). In-wound bacteria counts were sampled just prior to closingusing the tetrazolium stained membrane imprint (TSMI) method by pressing47 mm cellulose acetate and nitrate filter membranes onto the woundsurface for 20 seconds and transferring them to agar plates. The resultsof the simulated total hip arthroplasty surgeries in cadavers in whichthe device was either used (Test) or not used (Control) showed adramatic reduction in particulate counts at the surgical site throughoutthe duration of the simulated procedure (see FIG. 16). The averageparticulate was reduced by 93% in the Test condition (median=36, 95^(th)percentile=1960) versus the Control condition (median=1683, 95^(th)percentile=35,000).

Flow Simulations

The following Flow Simulation Examples refer to drawings that are blackline tracings of computer screen shot color graphics resulting fromcomputer simulations explained in the Flow Simulation Examples. Thecomputer program rendering the simulations employs graphics that use acolor spectrum to indicate flow line velocities, gradations from dark tolighter blues to dark to lighter greens to light to darker yellows tolight to darker oranges to light to darker reds indicating velocitiesthat increase with movement up the color spectrum, dark blue indicatingthe slowest velocity and dark red indicating the fastest. Sterile gasemitted from the emitter has velocity and in color the computer graphicsof the simulation program display this in the warm colors according toemergent velocity and velocity degradation with distance from point ofdischarge from the emitter, in some instances moving into the greens. Bycontrast, ambient air is essentially stationary until given velocity asit is drawn forward by the flow discharged from the emitter, and incolor the computer graphics show this in gradations in cool colors (fromdark to lighter blues to dark to lighter greens). In the black linedrawings of FIGS. 19-34, the lines are black line tracings of thecomputer screen shots, including the flow lines, and lacking color,several conventions are employed to distinguish the flow lines and theirvelocities. Flow lines of sterile gas discharged from the outlet of anemitter are shown in solid lines. Weight of a solid line is used torepresent velocity, lighter weights indicating a lesser velocity. Flowlines from ambient air are shown as dashed lines. Length of a dashsignifies velocity, lesser velocities being indicated by smaller lengthsof dash. Reference numerals in the series from 130 to 139 are used tosupplement the weighted solid and dash length line conventions. Thesereference numerals indicate velocities as explained in more detailbelow. As an aid to assist distinguishing numbers 130-139 representingvelocities from other numbers, reference numerals 130-139 are presentedin a serif font (Times New Roman) whereas the normal numbers arepresented in a san serif font (Arial).

The line drawing tracings illustrate the concepts involved in using ananatomical shape conforming emitter to apply a unidirectional coherentnon-turbulent flow field of essentially sterile gas substantiallyanatomically levelly onto a surface mimicking an anatomical surface of apatient, and illustrate emitters and flows not in conformity withconcepts of the invention. Flow Simulation Examples 1 and 2 showsimulations of flow using prior art devices. Flow Simulation Example 3shows an anatomically shape conforming emitter having outlet dimensionssubstantially the same as in the embodiments of FIGS. 1-4 with theemitter placed anatomically levelly on an emulated anatomical surface,and accords with the present invention. Flow Simulation Examples 4 and 5demonstrate that even using an emitter having an orifice outlet profileas in Flow Simulation Example 3, the concepts of our invention are notapplied because the embodiment either is not anatomically level with thesurface (Flow Simulation Example 4) or is not anatomically shapeconforming (Flow Simulation Example 5). Flow Simulation Example 6 showsanother example of an emitter that is not anatomically shape conformingand does not produce a flow that is anatomically level. As will be seenfrom these simulations, only Flow Simulation Example 3 provides anessentially sterile unidirectional coherent non-turbulent gas flowfield.

Flow Simulation Example 1 Prior Art—Flow Not Horizontally Level with theSurface and Not Sterile

Referring to FIGS. 17-19, a series of flow simulations are depicted thatemploy an emitter configuration of the type described in the article byThore M, et al.: Further bacteriological evaluation of the TOUL mobilesystem delivering ultra-clean air over surgical patients andinstruments, JOURNAL OF HOSPITAL INFECTION 63, 185-192 (2006), notedabove as similar to U.S. Pat. No. 3,820,536, configured and deployed asdescribed in that article and employing flow velocities described inthat article. The emitter outlet size is 0.55 meters (21.654 inches)wide, 0.4 meters (13.638 inches) high and has a central airflow zonewith a peripheral airflow zone 1.5 inches inset from the edges of theemitter. The peripheral zone is angled outwardly 25 degrees. The emitteris 0.681 meters (24.350 inches) above surface 102 and is inclined towardsurface 102 at a 60-degree angle. The arcuate surface 102 is an arcuatesurface of a segment of a circular horizontally disposed column 14.610inches in diameter in emulation of an anatomical surface of a surgicalpatient, such as a thigh. The length of the segment is 10.651 inches.The simulations were performed using a computer program “CFDesign”version 9.0 available from Upfront CFD run on an Intel based PC computerusing a Windows XP 64 bit operating system. The following parameterswere used for the program simulations: exiting velocity for the centralairflow zone was 0.5 m/sec (100 ft/min) and for the peripheral zone was0.3 m/sec (59 ft/min); a “wall” condition was set on the curved surface;and all other boundaries received P=0 (atmospheric) conditions. Meshsize was: 50 inches wide, 60 inches tall and 100 inches long. Thesimulation contained 359,866 fluid elements and converged after 325iterations.

FIG. 17 is an isometric depiction of the flow trace elements (solidlines) emerging from the emitter outlet 120 and passing over surface 102and also shows flow trace elements for ambient air (dashed lines) drawninto the area and given velocity by the fast flow discharged from theemitter outlet. FIG. 18 depicts the flow trace elements in a verticalplane through the center of the emitter 102. FIG. 19 depicts the flowtrace elements at an edge of emitter 120 closest to the viewer. Theemitter of FIGS. 17-19 is not anatomically shape conforming and thesimulated flow is not “level” and is not “anatomically level” withsurface 102. As illustrated by FIGS. 17-19, flow from the emitter 120(solid lines) is not horizontally level with surface 102, is scatteredalong surface 102, and large amounts of ambient air 109 (dashed lines)are drawn into the flow under the emitter onto surface 102. Thisdrawn-under ambient air would contaminate sterile gas emitted fromemitter 120. Ambient air 105 at the top of emitter 120 is drawn into theairflow and swept forward, increasing in speed.

Reference numerals 130-134 supplement the convention of weighted solidand dashed lines for illustrating velocities. Solid flow lines atvelocity 130 have a heavier weight than solid flow lines at a velocityof 131; solid flow lines at a velocity of 131 have a heavier weight thansolid flow lines at a velocity of 132; solid flow lines at a velocity of132 have a heavier weight than solid flow lines at a velocity of 133;and solid flow lines at a velocity of 133 have a heavier weight thansolid flow lines at a velocity of 134. As mentioned, faster ambient flowlines have longer dash lengths. The same reference numeral is used for agiven range of velocities whether the lead to the reference numeral isto a solid line or a dashed line. Nominal ranges of velocities for solidand dashed lines are indicated by reference numbers as follows:

Reference numeral Velocity (ft/min.) 130 from about 80 to about 100 131from about 60 to about 80 132 from about 40 to about 60 133 from about30 to about 40 134 from about 5 to about 30Flow lines having more than one reference number along their lengthindicate changing velocities along that length.

Flow Simulation Examples 2-6 Introductory Comments

In Flow Simulation Examples 2-6 and corresponding FIGS. 20-34, the flowsimulations used the same nominal emitter flow velocity (350 ft/min), soa higher series 135-139 of reference numerals indicative of higher flowvelocities are employed in FIGS. 20-34 to supplement the convention ofweighted solid lines and dashed lines for illustrating velocities.Nominal ranges of velocities for solid and dashed lines are indicated inFIGS. 20-34 by reference numbers as follows:

Reference numeral Velocity (ft/min.) 135 from about 280 to about 350 136from about 220 to about 280 137 from about 140 to about 220 138 fromabout 80 to about 140 139 from about 20 to about 80The same reference numeral is used for a given range of velocitieswhether the reference numeral leads to a solid line or a dashed line.Solid flow lines at a velocity of 135 have a heavier weight than solidflow lines at a velocity of 136, solid flow lines at a velocity of 136have a heavier weight than solid flow lines at a velocity of 137, andsolid flow lines at a velocity of 137 have a heavier weight than solidflow lines at a velocity of 138, and faster ambient flow lines havelonger dash lengths. Flow lines having more than one reference numberindicate different flow velocities along the length of the flow line.

Flow Simulation Example 2 Prior Art—Coanda Jet Effect, Flow HorizontalBut Not Sterile

Referring to FIGS. 20-22, a series of flow simulations are depicted thatemploy a rectilinear flat bottomed emitter 115 that is 8 inches wide and0.5 inches high (the dimensions of the flat nozzles depicted in U.S.Pat. No. 4,275,719 to Mayer, mentioned above) over a flat plate 202, asin a Coanda Effect for a jet emitted adjacent a flat surface. A space of0.375 above the flat plate was necessary for simulation stability. Thesimulations were performed using the same computer program as in FlowSimulation Example 1. The following parameters were used for the programsimulations: velocity condition at emitter outlet (exiting emitter) was350 ft/min; all other boundaries received P=0 (atmospheric) conditions.Mesh size was 16″ wide, 12″ tall and 24″ long. The simulation contained190,490 fluid elements and converged after 904 iterations

FIG. 20 is an isometric depiction of the flow trace elements emergingfrom the center vertical plane of the outlet of flat emitter 115 andpassing over surface 202. FIG. 21 depicts a side view of the flow traceelements in the vertical plane through the center of emitter 115, andFIG. 22 depicts the flow trace elements at the lateral edge of emitter115 closest to the viewer. As illustrated by FIGS. 20-22, flow fromemitter 115 is generally horizontal but is underlain by large amounts ofambient air 109 drawn under emitter 115 and forming part of the flowclosest to surface 202, contaminating the flow from emitter 115. As inFlow Simulation Example 1, ambient air 105 at the top of emitter 120 isdrawn into the airflow from the emitter and swept forward. Ambient air107 from the lateral side of emitter 115 is also drawn into the flow andswept forward.

Flow Simulation Example 3 Emitter is Anatomically Shape Conforming andFlow is Anatomically Level and Essentially Sterile

Referring to FIGS. 23-25, a series of flow simulations are depicted thatillustrate the performance characteristics represented by embodiments ofthe invention used in accordance with the concepts of the invention.FIGS. 23-25 depict traces of flow elements using an anatomically shapeconforming emitter a detailed construction of which is described inconnection with FIGS. 1-4. The flow simulation in FIGS. 23-25 is one inwhich the emitter 101 is substantially anatomically level with a surface102, which for illustration, is an arcuate surface of a segment of acircular horizontally disposed column, as in Flow Simulation Example 1.The emitter 101 conforms to the shape of surface 102, has a width of8.355 inches and center height of 1.890 inches. It has a surfaceconformable barrier 103 under the emitter undersurface that is 0.125inches thick. The arcuate surface is a segment of a circular column14.610 inches in diameter. The length of the segment is 10.651 inches.The simulations were performed using the same computer program as inFlow Simulation Examples 1 and 2. The following parameters were used forthe program simulations: velocity condition at emitter outlet (exitingemitter): 350 ft/min; a “wall” condition on curved surface; all otherboundaries received P=0 (atmospheric) conditions; mesh size: 16″ wide,12″ tall and 24″ long, containing 169,016 fluid elements. The simulationconverged after 339 iterations.

FIG. 23 is an isometric depiction of the flow trace elements emergingfrom the lowest arc of the emitter outlet 41 and passing along surface102. Reference numeral 135 indicates the exit velocity of flow lines inthe boundary band indicated by reference numeral 136, and referencenumeral 138 indicates the velocities of flow discharging from the bandindicated by 138 at the edge of outlet 41. Flow velocities near the edgeof outlet 41 in outer band 138 and next nearest band 136 have lessvelocity in the interior region 135 of outlet 41. FIG. 24 depicts theflow trace elements exiting in a vertical plane through the center ofemitter 101. FIG. 25 depicts the flow trace elements at an edge ofemitter 101 closest to the viewer. As illustrated by FIGS. 23-25, flowfrom the emitter 101 is unidirectional, coherent and non-turbulent, hasa boundary layer attached to the surface 102, e.g. at 104, and blockedby barrier 103, no airflow enters the flow field underneath emitter 101,i.e., between the emitter 101 and surface 102. FIGS. 24 and 25 show thatambient air 105 at the top of emitter 101 is entrained and swept alongthe top edges 106 of the flow field. FIGS. 23 and 25 show that ambientair 107 outside the lateral sides of emitter 101 is entrained as at 108along the lateral peripheries of the flow field. FIGS. 23-25 show thatthe 0.125 inch compressed thickness of barrier 103 between the lowermargin of the outlet of emitter 101 and surface 102 allows a tiny lowpressure area 113 to develop immediately adjacent the lower edge ofemitter 101 behind where the lowest flow elements for a boundary layerattach to surface 102, and a trace 110 of ambient air is drawn into lowpressure area 113 and is entrained in the flow field. This trace 110 isconsidered comparatively de minimus compared to the massive amounts ofambient air drawn into the flow immediately over the surface 102 in theprior art (Flow Simulation Examples 1-2) and in Flow Simulation Examples4-6 that do not conform to the concepts of the invention, and as deminimus thus not contaminating the sterile quality of gas flowed fromthe emitter to the extent it is no longer essentially sterile.

Flow Simulation Example 4 Emitter is Anatomically Shape Conforming andFlow is Horizontal But Emitter is Not Anatomically Level with theSurface so Flow is Not Essentially Sterile

Referring to FIGS. 26-28, a series of flow simulations are depicted thatemploy an emitter 101 of the same outlet configuration and dimensions asin FIGS. 1-4, but employing a thicker barrier 112 that is 2 inchesthick. The arcuate surface has the same configuration and dimensions asin the Flow Simulation Example 1 and 3. The simulations were performedusing the same computer program as in Flow Simulation Example 1-3. Thesame parameters were used for the program simulations as used in FlowSimulation Example 3, except that the simulation contained 169,016 fluidelements. The simulation converged after 309 iterations.

FIG. 26 is an isometric depiction of the flow trace elements emergingfrom the bottom of the emitter outlet and passing over surface 102. FIG.27 depicts the flow trace elements in a vertical plane through thecenter of emitter 101, and FIG. 28 depicts the flow trace elements atthe lateral edge of emitter 101 closest to the viewer. As illustrated byFIGS. 26-28, flow from the emitter 101 is unidirectional, coherent andnon-turbulent, and because of barrier 112 no airflow enters the flowfield underneath emitter 101, but the flow from emitter 101 is notattached to the surface 102. Emitter 101 is level in the sense of thatit is not inclined toward surface 102, and flow is at least initiallygenerally parallel with surface 102, but the lowest part of the gas flowfield from the emitter is not level with the surface 102 in the sensethat it is sufficiently higher than the anatomical surface that the gasflow does not attach to and form a boundary level with surface 102. Thusalthough emitter 101 is an anatomically shape conforming emitter, thatis, the lower margin of the outlet conforms to the cross sectionalcontour of surface 102, as does barrier 112, the emitter is notsubstantially anatomically level with surface 102.

As in FIGS. 24 and 25, in FIGS. 27 and 28 ambient air 105 at the top ofemitter 101 is entrained and swept along the top edges of the flowfield, but unlike in Flow Simulation Example 3, the lower margin of theoutlet of emitter 101 is so high over the surface 102 that the flow fromemitter 101 develops a large low pressure area 111 under the outlet,drawing substantial amounts of ambient air 107 turbulently into theinterior of the flow field, as shown in FIGS. 26-28. The substantialamounts of ambient air 107 drawn into the flow field are swept oversurface 102 beneath the flow field, and would contaminate a surgicalfield with particulates carried in ambient air, in contrast to the deminimus trace line in Flow Simulation Example 3.

Flow Simulation Example 5 Emitter is Not Anatomically Shape ConformingSo Flow is Not Essentially Sterile

Referring to FIGS. 29-31, a series of flow simulations are depicted thatemploy the same emitter 101 as in FIGS. 23-25, but without the barrier103 filling a space between the emitter and surface 102. A space of0.375 was necessary for simulation stability. Arcuate surface 102 hasthe same configuration and dimensions as in the Flow Simulation Example3. The simulations were performed using the same computer program as inFlow Simulation Example 3. The same parameters were used for the programsimulations as used in Flow Simulation Example 3, except that thesimulation contained 161,004 fluid elements. The simulation convergedafter 259 iterations.

FIG. 29 is an isometric depiction of the flow trace elements emergingfrom a vertical plane in the center of the emitter outlet and passingover surface 102. FIG. 30 depicts a side view of the flow trace elementsin a vertical plane through the center of emitter 101, and FIG. 31depicts the flow trace elements at the lateral edge of emitter 101closest to the viewer. As illustrated by FIGS. 29-31, flow from theemitter 101 is unidirectional, coherent and non-turbulent, but becauseno barrier exists blocking flow under emitter 101, ambient airflow 109enters underneath emitter 101 and contaminates the flow field, just asit did for Flow Simulation Examples 1 and 2. Because the barrier 103present in the emitter of Flow Simulation Example 3 is lacking, there isno undersurface so matching the shape of the anatomy where the emitterbody is to be affixed and ambient airflow is not substantiallycompletely prevented from penetrating underneath the emitter and asshown it does infiltrate under the emitter and enter the interior of thecoherent non-turbulent flow emergent from the emitter outlet.Accordingly the emitter in this Flow Simulation Example 5 is notanatomically shape conforming. FIGS. 29 and 30 are especially clear inshowing that ambient air drawn into the emitted flow field contributeslargely to the flow that forms a boundary layer on the surface, so theflow over the surface is not essentially sterile.

Flow Simulation Example 6 Emitter is Not Anatomically Shape ConformingFlow is Not Anatomically Level and Not Sterile

Referring to FIGS. 32-34, a series of flow simulations are depicted thatemploy the same emitter shape and dimensions as in Flow SimulationExample 2 but over an arcuate surface as in Flow Simulation Examples 1,3, 4 and 5, and further, unlike in Flow Simulation Example 2, theemitter is additionally supplied with a barrier 116 that substantiallyconforms to surface 102. However the lower edge or margin of the outletof emitter 115 is not anatomically level with surface 102 over the widthof the outlet. The lower margin of the outlet of emitter 115 is “level”with surface 102 only at the point of tangency at the apex of arcuatesurface 102. The barrier 116 has the same compressed thickness where theoutlet of emitter 115 is level at that tangent point as in FlowSimulation Example 3 but the barrier increases in thickness on bothsides of the point of tangency. The arcuate surface has the sameconfiguration and dimensions as in the Flow Simulation Examples 1, 3, 4and 5. The simulations were performed using the same computer program asin all the other Flow Simulation Examples. While the shape anddimensions of the emitter are different, the other parameters are thesame as used for the program simulations in Flow Simulation Examples 1and 2, except that the simulation contained 161,004 fluid elements. Thesimulation converged after 259 iterations.

FIG. 32 is an isometric depiction of the flow trace elements emergingfrom the bottom of the outlet of flat emitter 115 and passing oversurface 102. FIG. 33 depicts the flow trace elements in a vertical planethrough the center of emitter 115, and FIG. 34 depicts the flow traceelements at the lateral edge of emitter 115 closest to the viewer. Asillustrated by FIGS. 32-34, flow from emitter 115 is unidirectional andgenerally horizontal, and because of barrier 116 no airflow enters theflow field underneath emitter 115, but the sterile flow from emitter 115is attached to the surface 102 only in a vertical longitudinal planeperpendicular to the point of tangency of the surface 102. On eitherside of the vertical plane the sterile flow is increasingly not attachedto surface 102, because the lower margin or boundary of the orifice oroutlet of the emitter 115 is not essentially uniformly along its widthequidistant to the undersurface of the emitter (barrier 116) coming intocontact with surface 102. Thus although emitter 115 is has ananatomically shape conforming barrier 116, because the lower margin orboundary of the orifice or outlet of the emitter is not essentiallyuniformly along its width equidistant to the undersurface of the emitter(barrier 116) coming into contact with surface 102, emitter 115 is notan anatomically shape conforming emitter, as a consequence of which theflow is not substantially anatomically level with surface 102.

FIGS. 33 and 34 also show, as in FIGS. 21 and 22, that ambient air 105at the top of emitter 115 is entrained and swept along the top edges ofthe flow field, but unlike in Flow Simulation Example 2, the height ofthe lower margin of the outlet of emitter 115 over the surface 102 oneither side of the point of tangency at which the emitter is placedcauses the flow to develop a substantial low pressure area on both suchsides under the outlet that draws large amounts of ambient air 107 intothe flow field, as especially shown in FIGS. 33 and 34. Because the flowfield is not attached to the surface where the low-pressure areadevelops, the substantial amounts of ambient air 107 drawn into the flowfield are swept over surface 102 beneath the flow field, and wouldcontaminate a surgical field with particulates carried in ambient air.

CONCLUSION

We have described embodiments and methods to create a localized dynamicflow field of coherent non-turbulent sterile gas, approximately 0.5meters (approximately 20 inches) long, directly on and over a surgicalsite to protect the site from intrusion of ambient airborne particles.The embodiments and methods place an emitter of sterile gas on theanatomical surface of a patient adjacent the site of the surgicalincision substantially anatomically level with the anatomy at that site.The emitter is constructed to match the general anatomical surface ofthe patient adjacent the incision site, to adapt to the particular sizeof that anatomical surface, and to prevent entrainment of air andairborne particles beneath the emitter. The emitter emits aunidirectional coherent non-turbulent flow of sterile gas, which “hugs”the patient in the localized field and surrounds the surgical site. Bylocating this protective shield directly on the patient at the surgicalsite, the shield is placed under the surgical staff leaning over theincision and overhanging operating room equipment with the result thatsurgical staff, operating room equipment and others in the operatingroom are placed “outside” the protective shield. It is shown that thisvery effectively reduces the presence of airborne particulate andbacteria within the surgical shield. Additionally the localized flowfield becomes turbulent past the area of shield, with the result thatparticles riding the peripheries of the field are dispersed by theturbulence away from the surgical table and sterilized equipment outinto the operating room rather than remaining concentrated in a coherentflow passing over the sterilized equipment.

The above disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover allmodifications, enhancements, and other embodiments that fall within thetrue scope of the present invention, which to the maximum extent allowedby law, is to be determined by the broadest permissible interpretationof the following claims and their equivalents, unrestricted or limitedby the foregoing detailed descriptions of embodiments of the invention.

The invention claimed is:
 1. Apparatus for protecting a site of surgicalincision in the anatomy of a patient from ambient airborne microbes inan operating room in which the site is exposed to the operating roomatmosphere during surgery, comprising an anatomically shape conformableemitter configured (a) to emit sterile coherent non-turbulent gas, inone direction only, into ambient air in the operating room,substantially anatomically levelly with the anatomical surface of thepatient adjacent only one side of said site for flow of the emittedsterile coherent non-turbulent gas substantially anatomically levellyacross the site unidirectionally from said one side of site to anopposite side thereof, and (b) to block entry of ambient air under saidemitter into said flow.
 2. The apparatus of claim 1 in which saidemitter comprises: (a) an upper exterior surface and an undersurface,(b) a chamber within said surfaces, said chamber having an inlet adaptedto receive sterile gas from a source of sterile gas and an outlet spacedfrom said inlet, said outlet having a height and width predetermined toestablish a height and width of a zone for shielding a surgical sitefrom ambient airborne bacteria, and having a lower margin essentiallyuniformly along the outlet width equidistant to said undersurface andwherein a dimension of height between said outlet and said undersurfaceis such that when the emitter is affixed onto said anatomical surfacethe gas flow from the outlet is substantially anatomically level withthe anatomical surface of the patient across the width of the outlet,(c) porous media within said chamber proximate said outlet through whichsterile gas received in said inlet is passed to provide coherentnon-turbulent unidirectional flow from said outlet, and (d) a shapeconforming barrier in continuous contact with said undersurface alongthe width of said outlet for shape conforming placement of said emittersubstantially anatomically levelly on an anatomical surface to prevententrance of ambient gas between said undersurface of said emitter andsaid anatomical surface.
 3. The emitter of claim 2 in which said emitterfurther comprises a flat surface on at least a portion of said upperexterior surface of said emitter providing a tray for placement ofsurgical instruments, and a gas vent from the interior of said assemblyfacing and opening across said tray for passing sterile gas across saidtray to maintain a sterile field on said tray for said instruments. 4.The apparatus of claim 2 in which the underside of the emitter isincurvate.
 5. The apparatus of claim 2 in which said barrier iscompressible.
 6. The apparatus of claim 2 in which said porous media issituated within said chamber proximate said outlet through which sterilegas received in said emitter inlet is passed, said apparatus furthercomprising flow guides inside said emitter between said emitter inletand said emitter outlet, placed for distributing sterile gas evenlyacross said porous media.
 7. The apparatus of claim 2, furthercomprising: (a) a hose for attachment distally to a source of sterilegas and proximately to said emitter inlet, said hose having aflexibility allowing the emitter to be placed substantially anatomicallylevelly directly on a portion of a patient's surface anatomy adjacentand all to one side of said site of surgical incision, and (b) at leastone releasable fastener for releasably affixing said emitter to saidportion of anatomy substantially anatomically levelly and inanatomically shape conforming contact therewith.
 8. The apparatus ofclaim 7 in which said fastener comprises an adhesive strip on the sideof said barrier to be placed on said portion of anatomy.
 9. Theapparatus of claim 7 in which said fastener comprises at least one strapand strap fastener affixed to said emitter.
 10. The apparatus of claim 1in which said emitter has an undersurface so matching the shape of saidanatomical surface that when said emitter is affixed to said anatomicalsurface ambient airflow is substantially completely prevented frompenetrating underneath the emitter and entering the interior of saidcoherent non-turbulent flow.
 11. The apparatus of claim 10 in which saidemitter has an outlet for said sterile gas having a dimension of heightand width and has a lower margin essentially uniformly along the outletwidth equidistant to said undersurface and wherein a dimension of heightbetween said outlet and said undersurface is such that when the emitteris affixed onto said anatomical surface the gas flow from the outlet issubstantially anatomically level with the anatomical surface of thepatient across the width of the outlet.
 12. The apparatus of claim 11comprising a shape conforming barrier in continuous contact with said atleast a portion of said undersurface under said outlet along a width ofsaid outlet for shape conforming placement of said emitter directly onsaid anatomical surface to prevent entrance of ambient air between saidunderside and said anatomical surface.
 13. The apparatus of claim 12 inwhich said shape conforming barrier is deformable.
 14. The apparatus ofclaim 13 in which said shape conforming barrier is a compressible foammaterial adhered to said portion of said undersurface of the emitter.15. The apparatus of claim 11 in which the emitter comprises a moldedemitter body that generally conforms to a typical shape of an anatomicalsurface adjacent a said site and a shape conformable material affixed tothe underside of the molded body to provide a barrier substantiallycompletely preventing infiltration of ambient airflow underneath theemitter when the emitter is affixed on the anatomical surface.
 16. Theapparatus of claim 15 in which the emitter has an underside that isincurvate and an outlet for the gas flow that has a correspondinglyincurvate lower margin.
 17. The apparatus of claim 15 comprisingadhesive on an undersurface of said shape conformable material forreleasably affixing said emitter to said anatomical surface.
 18. Theapparatus of claim 15 comprising one or more straps for strapping saidemitter to said anatomical surface.
 19. Apparatus for protecting a siteof surgical incision in the anatomy of a patient from ambient airbornemicrobes in an operating room in which the site is exposed to theoperating room atmosphere during surgery, comprising an anatomicallyshape conformable emitter configured (i) to emit sterile coherentnon-turbulent gas, in one direction only, into ambient air in theoperating room, substantially anatomically levelly with the anatomicalsurface of the patient adjacent only one side of said site for flow ofthe emitted sterile coherent non-turbulent gas substantiallyanatomically levelly across the site unidirectionally from said one sideof the site to an opposite side thereof, and (ii) to block entry ofambient air under said emitter into said flow, said emitter comprising:(a) an upper exterior surface and an undersurface, (b) a chamber withinsaid surfaces, said chamber having an inlet adapted to receive sterilegas from a source of sterile gas and an outlet spaced from said inlet,said outlet having a height and width predetermined to establish aheight and width of a zone for shielding a surgical site from ambientairborne bacteria, and having a lower margin essentially uniformly alongthe outlet width equidistant to said undersurface and wherein adimension of height between said outlet and said undersurface is suchthat when the emitter is affixed onto said anatomical surface the gasflow from the outlet is substantially anatomically level with theanatomical surface of the patient across the width of the outlet, (c)porous media within said chamber proximate said outlet through whichsterile gas received in said inlet is passed to provide coherentnon-turbulent unidirectional flow from said outlet, (d) a shapeconforming barrier in continuous contact with said undersurface alongthe width of said outlet for shape conforming placement of said emittersubstantially anatomically levelly on an anatomical surface to prevententrance of ambient gas between said undersurface of said emitter andsaid anatomical surface, and (e) a flat surface on at least a portion ofsaid upper exterior surface of said emitter providing a tray forplacement of surgical instruments, and (vi) a gas vent from said chamberfacing and opening across said tray for passing sterile gas across saidtray to maintain a sterile field on said tray for said instruments.